There are several issues that professional pilots have with the concept of "buying a job":
1) Skill level. There are a LOT of valuable lessons to be learned in general aviation between 250 and 1000 hours. You cannot learn nearly as much in the the right seat of an airliner because 121 ops are conducted in a relatively sterile environment. You have radar coverage, TCAS, and class B to protect you from bug-smashers, system redundancy turns most equipment failures into a simple paperwork drill, and most weather is reduced to five switches: three anti-ice switches and the radar power and tilt switches. Insurance companies historically have required 1000 hours for commercial pilots. They base their requirements on real-world data accumulated over the years. They are about as unbiased as you can get...they WANT to take your money.
2) Those folks who have worked their way up have a much better appreciation for the rigors and challenges of our profession...we KNOW what we are worth. Low-time pilots get sucked into this attitude that they are lucky to have a job at all...they all figure out the reality in a few years, but by then it's too late. Many young people still have this perception that any amount of dues paying is worth it to get to that major job in the long run...may have been true when you could make $10M over your career at one of the big six, but those days are LONG gone.
3) Everyone but the military guys paid for the training needed for their FAA certificates. This is normal for licensed professionals in almost any field. However, pilots should NOT have to pay for airline or aircraft-specific training PERIOD. People who do are undercutting the rest of us. The companies would like us to pay $12-15,000 every time we upgrade to new equipment, and $2000 every six months when we do our PC's...not a place we want to go. I am not a a fan of SWAs type rating policy either.
If you have little or no 121 experience, I absolutely guarantee you that a few years down the road your opinion will be very similar to my own. If you take a $18/hour airline job, go in with the attitude that you are going to fix the payscale or WALK OUT at the next contract. BTW $18/hour on an airline payscale translates to about $6/hour for actual work time. You don't get paid unless the airplane is actually moving.